N2O concentrations measured on water bottle samples during Akademik Tryoshnikov cruise Arctic Century 2021 Expedition (AT21), Arctic Ocean

Sea water samples were collected as part of the Arctic Century Expedition, which took place in the Kara Sea (Arctic Ocean) aboard the research vessel Akademik Tryoshnikov between August and September 2021. A total of 27 stations were sampled for full-depth profile measurements of nitrous oxide (N₂O). N₂O samples were collected from the Niskin bottles using a Tygon® tube and transferred into borosilicate 60 ml serum bottles. Samples were poisoned by introducing 60 μL saturated mercury chloride (HgCl₂) solution. The bottles were sealed with isobutyl stoppers and capped with aluminium crimps. The bottles were kept in dark at room temperature until analysis at home laboratory. Measurements of N₂O concentration were conducted using the headspace technique described by Weiss (1981) and Upstill-Goddard et al. (1996). Briefly, approximately 25 mL of the sea water sample was replaced by ultra-pure N gas (AirLiquide Belgium®, Alphagaz 2, N₂ ≥ 99.9999%), followed by manual agitation and overnight equilibration in a water bath at room temperature. A 12 mL extraction from the headspace was injected into an SRI Instrument Model 8610C Gas Chromatograph with Electron Capture Detector (ECD), for analysis. The calibration was performed using precision gas mixtures containing N₂O, CH₄, CO₂, and N₂, provided by AirLiquide Belgium®. Temperature and salinity data from water bottle samples were provided by the Gangnus et al. (2022) dataset (doi:10.1594/PANGAEA.947808). The data are provided by the Arctic Century Expedition, a joint initiative led by the Swiss Polar Institute (SPI), the Antarctic and Arctic Research Institute (AARI) and GEOMAR Helmholtz Centre for Ocean Research Kiel (GEOMAR) and funded by the Swiss Polar Foundation, AARI, Minobrnauki (CATS RFMEFI61619X0108) and BMBF (CATS 03F0831).